Various night vision devices are well known in the art. These devices are primarily, but not exclusively, used by law enforcement and military personnel to improve a user's ability to see during activities performed in low light conditions. Typically, night vision devices operate within the range of the electromagnetic spectrum where incident light has a wavelength of or between 400 to 1000 nanometers (nm). Many night vision devices incorporate a component known as an image intensifier. An image intensifier is a cylindrical assembly inside a tubular housing which multiplies or amplifies the amount of incident light it receives at one end, and outputs or transmits this amplified light directly to an ocular system located at its other end. The ocular system receiving the amplified or intensified light may be a camera or camcorder equipped with a sensor such as a CCD chip or like means, or in the case of specially adapted binoculars or telescopes, the human eye.
According to the present art of imaging systems, the incorporation of image intensifiers into an optical system always introduces optical anomalies and geometrical distortions. Typical of these optical distortions is the anomaly known in the art as "vignetting". Vignetting is illustrated in FIG. 1 and refers to the tunnel vision effect that occurs when images of differing format sizes are received by an optical system having a fixed image format. Invariably, vignetting distortions produce a dark or gray ring of non-illumination along the outer edge of the image. This ring of non-illumination is output onto part of the active circular area of the host camera or camcorder that could otherwise receive and record the viewed object or activity.
The present art of eliminating or preventing image distortions in an intensified imaging system makes use of various methods and techniques but is expensive to manufacture and cumbersome to implement. One method of correcting optical anomalies and geometrical distortions comprises means of an expensive tomography system which establishes an image's frame through the use of a computer and calibration object and then corrects vertical and horizontal distortions according to correction values that have been generated by the calibration process and stored in a computer. Another method has been to apply expensive electronic video hardware which applies vertical and horizontal blanking techniques which must be calibrated to achieve the exact superposition of multiple images to cancel or correct distortions. A third means has been the use or application of mirror subassemblies to split a color lens image into separate images and then electronically filter the separate images according to different requirements prior to recombining the images on a display monitor. Furthermore, geometric distortion-free images have been observed and recorded through an image intensifier by incorporating electronic sweep control circuits to alter the sweep pattern such that the electronic image representations generated by the video camera are distorted in a manner that is complementary to and cancels the distortion created by the image intensifier. As said before, each of these methods is expensive to manufacture and costly to implement. Some require a non-mobile or stationary environment to observe the object or activity under scrutiny. As a result of their cumbersome nature, the logistics of using such systems prohibits their application in a law enforcement or military environment.
Due to the frequency and various conditions under which the aforementioned users engage in nocturnal observations, a variety of image intensifiers are commercially manufactured. However, given the complex nature and construction of the individual components which comprise an image intensifier, it is cost prohibitive for a night vision manufacturer to produce a wide variety of image intensifying products to satisfy all the specific and fragmentary needs of the law enforcement and military markets. This economic constraint is made more acute by the fact that each different image intensifier is only capable of amplifying or intensifying images according to its particularly fixed image format. The fixed image format of an image intensifier is dictated by the mechanical dimensions and parameters of its lenses and accompanying optical apparatus which comprise the cylindrical assembly inside its tubular housing. As a method of distinguishing between the various sizes of image intensifiers, practitioners in the night vision art classify image intensifying hardware according to the diagonal measurement of the circular active area of the tubular housing. Simply put, this diagonal measurement determines the image format size of the image intensifier.
Similarly, other optical systems such as commercially available cameras or camcorders are manufactured in a wide and diverse variety. Because of larger economies of scale as well as less expensive construction costs of the necessary modules and related components, manufacturers of these photographic or video products can sustain the production of many various models which satisfy the specific needs of users despite the fact that each of these optical devices is also only able to produce images according to its particularly fixed image format. These optical products are typically offered for sale to ordinary persons to observe and record events which occur in daylight, near daylight or incandescent interior light conditions. Using the language of practitioners in the night vision industry, products which are only able to observe and record activities in daylight or near daylight conditions are referred to as "unintensified systems" because they are not primarily or especially designed to make use of the reduced light that is present during non-daylight hours. As one might expect, the image format size of an unintensified camera or camcorder system is dictated by the mechanical dimensions and parameters of the lenses and accompanying optical apparatus which comprise the means by which the camera or camcorder views or receives optical images. As a method of distinguishing between the various sizes of camera or camcorder products, practitioners in the art of photographic or video cameras classify optical hardware according to the diagonal measurement of the circular active area of the original objective lens assembly. In short, this diagonal measurement indicates the camera's or camcorder's image format size.
Given the nature of the imaging system art, any method or apparatus which easily and inexpensively incorporated the capabilities of an image intensifier with commercially available cameras or camcorders, without introducing the geometrical distortions that are inherent in an intensifier based imaging system, would be a welcome development. To this end, the present invention provides a night vision device wherein an unintensified imaging system is adapted to observe and record nocturnal activities by mechanically inserting means of an image intensifier and adjacent image correcting modules or subassemblies between the host camera's original objective lens system and the host camera itself. The adjacent image correcting modules or subassemblies are especially needed because of the particularly limited variety of image intensifiers that are presently available and the fact that optical distortions occur whenever an image intensifier having a fixed image format size is coupled with an unintensified lens system or lens assembly that has been designed to output images having a different image format size. These optical anomalies and distortions are geometrical in nature and occur primarily because the image output by the original objective lens system of the unintensified host camera or host camcorder fails to make use of the entire circular active area of the lenses and accompanying optical apparatus which comprise the image intensifier. Similarly, additional geometrical distortions and optical anomalies are produced whenever an image intensifier outputs an intensified image onto a lens system which has been designed to receive images of a different format size.
The present invention provides a new and inexpensive method and apparatus which prevents and eliminates optical anomalies and geometrical distortions.